Abstract
BackgroundTransmission of Mycobacterium tuberculosis (M. tuberculosis) complex could be possible between farmers and their cattle in Ethiopia.Methodology/Principal FindingsA study was conducted in mixed type multi-purposes cattle raising region of Ethiopia on 287 households (146 households with case of pulmonary tuberculosis (TB) and 141 free of TB) and 287 herds consisting of 2,033 cattle belonging to these households to evaluate transmission of TB between cattle and farmers. Interview, bacteriological examinations and molecular typing were used for human subjects while comparative intradermal tuberculin (CIDT) test, post mortem and bacteriological examinations, and molecular typing were used for animal studies. Herd prevalence of CIDT reactors was 9.4% and was higher (p<0.01) in herds owned by households with TB than in herds owned by TB free households. Animal prevalence was 1.8% and also higher (p<0.01) in cattle owned by households with TB case than in those owned by TB free households. All mycobacteria (141) isolated from farmers were M. tuberculosis, while only five of the 16 isolates from cattle were members of the M. tuberculosis complex (MTC) while the remaining 11 were members of non-tuberculosis mycobacteria (NTM). Further speciation of the five MTC isolates showed that three of the isolates were M. bovis (strain SB1176), while the remaining two were M. tuberculosis strains (SIT149 and SIT53). Pathology scoring method described by “Vordermeier et al. (2002)” was applied and the average severity of pathology in two cattle infected with M. bovis, in 11 infected with NTM and two infected with M. tuberculosis were 5.5, 2.1 and 0.5, respectively.Conclusions/SignificanceThe results showed that transmission of TB from farmers to cattle by the airborne route sensitizes the cows but rarely leads to TB. Similarly, low transmission of M. bovis between farmers and their cattle was found, suggesting requirement of ingestion of contaminated milk from cows with tuberculous mastitis.
Highlights
M. tuberculosis and M. bovis are amongst the most important pathogens from the M. tuberculosis complex (MTC), a highly related group of mycobacteria that cause TB in humans and other mammals [2]
The overall herd prevalence was 9.4% at cut-off .4 mm and 20.8% at cut-off .2 mm. At both cut-off values the comparative intradermal tuberculin (CIDT)-positive herd prevalence was significantly greater in herds owned by households with TB patients than in herds owned by TB free households living in the same village
The result of this study indicated that neither transmission of M. tuberculosis from man to cattle nor of M bovis from cattle to man could be demonstrated
Summary
M. tuberculosis and M. bovis are amongst the most important pathogens from the MTC, a highly related group of mycobacteria that cause TB in humans and other mammals [2]. M. tuberculosis is mainly considered as a human pathogen causing active TB in approximately eight million people every year [3], whereas M. bovis has a broader host range responsible for TB in domestic and wild animals [4]. It is well established that M. bovis infects humans, causing zoonotic TB in humans [5]. Smear positive cases are infectious and could be the sources of infection for healthy humans and animals. The main routes of M. bovis transmission from infected animal to humans are believed to be through ingestion of raw milk and/or inhalation of aerosol from diseased animal, mainly in settings where pasteurization of milk is not widely established. Transmission of Mycobacterium tuberculosis (M. tuberculosis) complex could be possible between farmers and their cattle in Ethiopia
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